1. Field of the Invention
The invention is directed to a process for the color transformation of the color stimulus specifications of image points of a color video system in which every color stimulus specification can be represented by components of a color vector within a color stimulus specification region which contains an achromatic point and is determined by input-side primaries of a signal source and in which image-side primaries whose color stimulus specification region likewise contains the achromatic point are used for displaying the image points, wherein at least one color stimulus specification of this color stimulus specification region lies outside the color stimulus specification region of the input-side primaries and a transformation is carried out for generating components referred to image-side primaries (R", G", B") and image-side components of negative intensity are suppressed at their occurrence. The invention is further directed to a color video system for showing color image points with an input circuit for generating and/or taking over color value signals associated with input-side primaries for a color stimulus specification region containing an achromatic point, with an image forming device for generating image points of a color video picture based on image-side primaries whose color stimulus specification region contains the achromatic point and at least one color stimulus specification outside the color stimulus specification region of the input-side primaries, and a matrix circuit which is connected between the input circuit and the image forming device and which transforms input-side color value signals into image-side color value signals for the image points of the image forming device.
2. Description of the Related Art
Color transformations in television reception for adapting transmitted color value signals to the phosphors of picture tubes are known, for example, from the book by Heinwig Lang, "Farbmetrik und Farbfernsehen [Colorimetry and Color Television]", R. Oldenbourg Verlag, Munich, 1978. The matrix transformations in the color space indicated in this reference can be used, for example, when a video picture with primaries based on the FCC standard is transmitted for color-correct display on a picture tube provided with phosphors based on the EBU standard. The FCC standard and EBU standard differ substantially in the green region so that color matching is required for color-correct display.
While the color stimulus specification regions do not differ from one another very much in this type of application, a matrix transformation is essential in laser projection systems because the wavelengths are monochromatic and the associated color vectors in the CIE diagram lie on the spectral curve plot. Projection systems of this kind are known from "Large Screen Laser Color TV Projector", Yahiko Yamada et al., Proceedings of 6th International Quantum Electronics, 1970, and from DE-PS 43 06 797. This patent is primarily concerned with correct color stimulus specification reproduction of a television picture transmitted, e.g., in EBU standard with lasers whose wavelengths determine the image-side primaries.
As in the first commercially available television receivers with picture tubes, such color video systems could also include the possibility of adjusting the signal level of the red, green and blue signals so that the color picture can be changed slightly to suit the taste of the user. However, this covers only the region of color hues and color saturations which are provided by the input-side primaries.
In the area of advertising and marketing, for example, it would also be desirable to have color video systems which could show color hues different from or colors with fuller saturation than those determined by the range of color stimulus specifications on the input side. In the presently known state of the art, for example, advertising videos could be played on one of the laser projection devices mentioned above, which videos must be recorded with special cameras or be processed subsequently so that a greater color stimulus specification region is accessible. Further, it would then be necessary to convert the laser projection devices in order to make available the greater color stimulus specification region for this application. Such steps are very costly because of the special devices required. As a result, even in the field of advertising where large amounts of money are generally available, this possibility has not been made use of.